The present invention relates to a manufacturing process of a superconducting wire with a heat treatment and a retainer for conducting a heat treatment, and more particularly, it relates to a technique for conducting heat treatment of a long length superconducting wire having a high critical electric current density.
Applications utilizing a magnet, such as magnetic resonance imaging (MRI) and superconducting magnetic energy storage (SMES), are recently under development. The copper wire constituting the magnet is being replaced by a superconducting wire. The long length superconducting wire having superconducting characteristics is required for the applications and an electric power cable application.
A typical superconducting wire is produced from a superconducting material, such as NbTi or an oxide superconducting material, by forming with a metallic sheath, and then subjected to heat treatment. The oxide superconducting wire is typically produced in such a manner that an oxide superconducting material or raw material powder thereof is filled into a metallic sheath, and a metallic sheath wire is formed by a plastic deformation process, such as wire drawing or rolling, which is then subjected to heat treatment. In the production of the long length superconducting wires, the said wires are coiled to conduct heat treatment efficiently. Because jointing technique of metallic sheathed superconductor wire has not yet been developed and the characteristics at the jointing part are remarkably deteriorated, it is an important developmental aspect to increase the length of the metallic sheathed superconducting wire.
Another important developmental aspect of the long length metallic sheathed superconducting is the heat treatment. The metallic sheath wire expands and shrinks by heat treatment. In order to conduct heat treatment of the metallic sheath wire without deterioration of the characteristics of the metallic sheath wire, the metallic sheath wire must to move freely without restriction during heat treatment.
Furthermore, there are cases where the superconducting wire is often locally blistered during heat treatment to cause considerable deformation (hereinafter, the phenomenon is referred to as xe2x80x9cwire blisterxe2x80x9d). The cause of the wire blister includes heat expansion of a gas inside the wire. At the part where the wire blister occurs, the critical electric current density Jc is lowered. It has been qualitatively known that the gas suffering the heat expansion to cause the wire blister includes CO2, H2O and O2.
Moreover, there are cases where the long length metallic sheath wires in contact with each other stick together. In particular, in the case where Cu, Al and Ag of high purity are used as a material of the metallic sheath, the metallic sheath wires tend to stick together.
As a first means for solving the problems, Japanese Patent Laid-open No. Hei6-243745, for example, discloses a technique proposing a method, in which metallic sheath wire is stacked with an intervening material not reacting with the wire, such as a commercially available ceramic tape, and is wound on a core in a pancake form. The term xe2x80x9cwound in a pancake formxe2x80x9d used herein means that the metallic sheath wire is densely wound in a coil form, and the term xe2x80x9cpancakexe2x80x9d used herein means the metallic sheath wire densely wound.
A second means for solving the problems proposes a method in which a fixture having a disk shape with a groove extending spirally on a flat surface thereof is provided, and the metallic sheath wire laid in the groove is subjected to heat treatment (described, for example, in Japanese Patent Laid-open No. Hei 4-292810), a method in which a heat resistant paint mainly comprising a silicone resin is coated on the surface of the metallic sheath wire, and a heat resistant coating is formed by heat treatment, which is then subjected to heat treatment, and a method in which a spacer separating the metallic sheath wires is stacked with the metallic sheath wire, which is then directly wound to overlap on a cylindrical fixture.
In the first means, however, there are restrictions on the size of the plate carrying the pancake, which is the metallic sheath wire wound in a pancake form, and the size of the furnace, in which the pancake is subjected to the heat treatment.
In the second means, in using the fixture having a groove spirally extending, because the metallic sheath wire is subjected to heat treatment in the groove spirally extending, there are restrictions on the size of the fixture having the groove and the size of the furnace for the heat treatment thereof, and it is unsuitable for heat treatment of the superconducting wire exceeding 100 m.
An object of the invention is to solve the problems and to provide a process for producing a long length superconducting wire having a high critical electric current density.
A first invention relates to a process for producing a superconducting wire comprising the steps of: inserting a metallic sheath wire, which is formed by complexing superconducting material or raw material powder thereof and a metal, in a metallic tube having an inner diameter larger than an outer diameter or a width of the metallic sheath wire; and conducting heat treatment of the metallic sheath wire under such a condition in that the metallic sheath wire is inserted in the metallic tube and wound to overlap on a cylindrical fixture. (Hereinafter xe2x80x9ccomplexxe2x80x9d or complexingxe2x80x9d means form or forming a composite material.) The metallic sheath wire is inserted in the metallic tube to prevent it from contact with the metallic sheath wire. When the metallic sheath wire inserted in the metallic tube is wound on a cylindrical fixture, the metallic sheath wire can freely move without restriction in the metallic tube even at the part forming a step where the metallic tube runs up to an upper layer from a lower layer, and the long length metallic sheath wire can overlap the cylindrical fixture without causing curvature or partial distortion of the metallic sheath wire.
Furthermore, the metallic sheath wire inserted in a metallic tube can be easily obtained by subjecting a long length metallic plate to deformation processing into the metallic tube, and simultaneously inserting the metallic sheath wire into the metallic tube, and the long length superconducting wire can be obtained by winding to overlap a cylindrical fixture, followed by conducting heat treatment.
According to the process, the metallic sheath wire suffers no deformation, such as curvature, even when heat treatment is conducted, and therefore the long length oxide superconducting wire having a high critical electric current density can be produced.
When heat treatment is conducted by controlling the atmosphere inside the metallic tube, into which the metallic sheath wire is inserted, the critical electric current density, on important characteristic of a superconducting wire, can further be improved.
Furthermore, by making a vacuum atmosphere inside the metallic tube, defects, such as blisters of the metallic sheath part of the superconducting wire, can be prevented, so as to obtain the long length superconducting wire.
A second invention relates to a process for producing a superconducting wire, in which even when two or more pancakes each comprising a metallic sheath wire wound in a form of a coil are stacked and subjected to heat treatment, problems, such as deterioration in characteristics, do not occur. That is, the process comprises a step of conducting heat treatment of the two or more stacked pancakes each comprising a metallic sheath wire wound in a form of a coil by using separating means that substantially does not restrict the behavior of the metallic sheath wire for stacking the two or more pancakes in a manner such that the adjacent pancakes are not in contact with each other. According to the process, two or more stacked metallic sheath wires can be treated without interference, and thus space saving can be realized. One of the means of heat treatment without interference of the two or more stacked metallic sheath wires is to apply a protective layer which is provided between the metallic sheath wires to prevent of movement of the metallic sheathed wire without restriction. Because the behavior of the adjacent metallic sheath wires inside the pancake are substantially not restricted by a protective layer, the problems occurring when the metallic sheath wire is restricted, such as deterioration and unfavorable sticking and deformation of the metallic sheath wire, can be resolved. And handling of the metallic sheath wire is also improved.
In the protective layer a spiral groove is provided to lead the metallic sheath wire to another pancake through the spiral groove provided substantially without restriction. Through the groove a superconducting wire having a long single wire length can be treated without termination and adverse effects caused by the restriction, so as to produce the superconducting wire.
The invention also involves a process for treating comprising heat treatment and a retainer for the treatment.
Furthermore, by heat treatment a metallic sheath wire under the suitable conditions such as an oxygen partial pressure, the temperature, the total pressure and the temperature increasing time, a good superconducting wire having an excellent critical electric current density and reduced wire blister formation can be produced.